at86rf525b ATMEL Corporation, at86rf525b Datasheet - Page 5

• Manufacturer Part Number: at86rf525b
• Description: 2.5ghz Wimax Transceiver
• Manufacturer: ATMEL Corporation

Functional Description
5189A–WiMAX–9/07
The AT86RF525B is based on the IEEE 802.16-2004 standard. This product will provide trans-
mit, receive, and frequency synthesis functions using the OFDM modulation schemes, as
defined in the above specifications.
The AT86RF525B consists of a frequency-agile RF transceiver intended for use in 2.5GHz
licensed bands at data rates up to 26Mbps.
Configuration and control registers and a bi-directional data communications interface are avail-
able to communicate with existing baseband devices from different vendors. The AT86RF525B
addresses the requirements of base station (BS) as well as subscriber stations (SS) equipment.
The device will operate down to 3.0V.
The AT86RF525B is fabricated in Atmel’s AT46000 advanced SiGe BiCMOS process technol-
ogy and is assembled in a 8mm x 8mm 56-lead QFN package.
RX Path
The differential low noise amplifier (DLNA) makes use of a differential bipolar stage with resistive
emitter linearization. For digital gain control operation the DLNA supports the four gain modes 0,
6, 12, and 18dB. The linearity improves as the gain is reduced.
The differential inphase quadrature phase mixer (IQMIX) utilizes a differential bipolar stage with
emitter degeneration for the best linearity performance. A complex driving LO source is chosen
for optimal LO leakage cancellation. The IQMIX has 4, 10, 16, and 22dB of switchable gain.
The receive poly phase filter (RXPPF) is designed as a frequency shifted leapfrog structure. The
filter provides three different bandwidths at three different center frequencies. The bandwidth of
this filter is tuned by a built-in self-test (BIST). The PPF filter cap values are automatically
adjusted upon power-up. The cap tuning values can be recalled via SPI. Image rejection is also
calibrated upon request via SPI.
There are also three digitally controlled gain amplifiers (DGA1-3) available to provide the neces-
sary amplification for the receive signal. Each stage supports the four gain modes 0, 6, 12, and
18dB respectively. An additional fine gain stage DGB enables gain tuning of approximately ±
6dB in 0.76 dB steps. An output buffer with gain offset matches the voltage swing of the radio to
the respective Baseband input stage.
The gain control is complete digital and affects LNA, MIX, and the three DGAs by using the
same granularity for each stage. The BB/MAC provides the gain vector at a separated serial
interface.
Fast TX/RX switching is possible via TX/RX switch input pins controlled by BB/MAC.
The low-IF conversion receiver does not have to amplify DC signals, but the gain setting process
produces different offsets in gain stages. An offset correction takes place after each gain step in
the receiver to prevent signal saturation. Every stage has an individual offset correction circuit to
maintain the correct overall dynamic range. The DC feedback (DCFB) works as an output offset
compensation network, which depends on actual gain setting.
The internal gain control operation is optimized for fixed target amplitude. To adapt to different
application requirements, the IQ Output Buffer DGB has a programmable gain offset from –
1.5dB to 6dB in increments of 0.76dB. This allows the nominal output voltage to be set between
180mVp and 650mVp. The gain is controllable via the register setting. The IQOB is able to drive
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